I. Field of the Invention
The present invention relates generally to butterfly valves and more particularly to a butterfly valve having an improved stub shaft to disc connection between the valve shaft and the valve disc. The improvement allows for easy removal and replacement of the valve shaft without invasion of the valve housing or flow line.
II. Description of the Related Art
Butterfly valves have historically been provided with one of two general types of connections between the actuator shaft and the valve disc. In one type of connection the disc includes a portion of increased thickness running longitudinally down the center of the disc and the actuator shaft is passed completely through the center of the disc and pivoted for rotation at the top and bottom of the valve. While such connections have been generally successful, they suffer from the disadvantage of being relatively expensive due to increased material and machining costs and also suffer from the disadvantage that a somewhat increased restriction to flow is presented when the valve is in the open position. A second general type of actuator shaft connection has been generally called a stub shaft connection. In stub shaft butterfly valves the disc includes portions of increased thickness (hubs) at the top and the bottom of the disc only. The actuator shaft is partially inserted into the hub at the top of the disc and a small shaft is inserted into the bottom hub of the disc. Such stub shafts have been connected to the disc in a variety of manners. In some instances the shafts have been pinned or bolted to the disc. Another approach has been to use a broached type connection such as a square connection or a hexagonal connection. Such connections have been subject to the disadvantages of leaking, providing protuberances into the flow stream, or looseness of connection resulting in a backlash, making it difficult to close the valve tightly, providing poor control with automatic actuators, or even permitting shaft blow out. Another type of connection which is known and which tends to overcome some of the aforementioned difficulties is a knurled or upset interference fit between the shaft and the valve disc. In this type of connection the shaft is provided with projections on one end thereof, which when forced into contact with the hole in the top of the disc, tends to radially deform the hole thereby resulting in an interference fit. This type of connection has suffered from the disadvantage that where a good connection has been made, high stress is created in the valve disc, which is usually nodular iron or stainless steel, thereby increasing the possibility of failure of the valve disc. These high stress levels are required because the disc hub stresses must create a high compressive frictional force in order to fully transmit the valve shaft torque in addition to preventing backlash and preventing the shaft from blowing out due to normal or abnormal internal pressures. While the disc hub may be made larger to reduce the stresses, this increases the cost of material. Furthermore, in those instances where the interference fit is not tight enough, valves may fail under pressure by forcing the shaft axially out of the hole, or by the interference connection being inadequate to transmit the required torque from the shaft to the disc.
Additionally, in the types of connections mentioned above, there is the potential problem, when using automated shaft drive systems, that the valve disk may become stuck or frozen in a given position in the flow line and create a situation where the shaft driving mechanism, such as an electric motor, is working against constant resistance over a period of time to free the stuck valve disc. This may lead to over heating of the motor which may result in burn out and destruction of the motor, thereby destroying expensive equipment and creating a fire hazard especially around flammable flow line materials. The costs in both replacement and repair materials as well as the concomitant down time associated with such a scenario are obvious.
Boos, in U.S. Pat. No. 3,539,148, discloses upper and lower split mounting pins for center pivoting the valve disc within the valve body, in combination with a solenoid actuator shaft. However, the pins are not easily removable.
In U.S. Pat. No. 3,701,362, to Reese, a butterfly valve housing assembly is disclosed, for indicating exteriorly, the open or closed position of the butterfly valve, by interconnection between the vane, drive shaft and outside indicator.
Barthelemy et. al. in U.S. Pat. No. 4,225,114, discloses a spline assembly on one end of the shaft for securing an actuator shaft to the hub of a valve disc of a butterfly valve. The assembly is a permanent connection formed by a pressure fit, wherein the splines cut grooves in the hub. The shaft, once inserted in the hub bore cannot be removed.
Another U.S. Pat. No. 4,303,094, to Rothwell, discloses a plastic coating of corrosive resistant composition bonded to the bearing means contained within the shaft bore of a butterfly valve assembly, thereby enhancing the longevity of bearing life.
Tsuchimoto et. al. in U.S. Pat. No. 4,697,615, discloses a butterfly valve, for controlling high-temperature fluid flow. Both the valve stem and valve disc, which are ceramic, are integrally formed as a unitary piece.
U.S. Pat. No. 4,944,325, issued to Baldwin et. al. discloses an erosive fluid butterfly valve, the valve comprising a housing formed by two flanged frustoconical body segments joined at their widest ends. The shaft is not readily removable.
Yohner, in U.S. Pat. No. 5,125,624, discloses a stem and disc arrangement; that is interfitted by slots. However, the purpose of this arrangement is to allow sufficient "play" in the slots, so that another "bonding means" such as a weld bead may be used to permanently join the disc and stem.
In U.S. Pat. No. 4,699,357, issued to Sisk, there is disclosed a butterfly valve housing having apertures diametrically aligned therein and counterbored, with the valve shaft passing completely through the valve disc and seating into both apertures so as to furnish a positive disc control during continuous industrial applications of the valve.
All of the aforementioned shaft-disc connections share a disadvantage in that the shaft is either permanently attached to the disc, such as by interference or compression fit, or is alternatively mounted to the disc by anchoring means such as bolts and the like. These types of connections require an invasive procedure into the flow line and disc valve housing in order to repair or replace a shaft. This necessitates the shut down of the flow line along with the disassembly of the valve disc housing structure. The economic disadvantage of this "down-time" for repair is obvious. The likelihood of contamination of surrounding environments by toxic flow line materials and the requisite decontamination and clean up costs as well as the danger to health due to worker exposure are also disadvantageous.